This invention relates to fluorescent electric discharge lamps of the type commonly used as a source of artificial illumination.
It is now recognized that natural electromagnetic radiation from the sun and sky is an important environmental element affecting the health, growth and development of plants, animals and human beings. Also, it has been recognized that unnatural man-made radiation sources including, but not limited to artificial light sources, may constitute health and safety hazards if they emit radiation which has substantial energy distortions at various wavelengths as compared with natural radiation under which life on earth has evolved. The term "light pollution" has been used in describing the biological effects of light from artificial light sources whose radiations are characterized by such distortions. Since visible light lies in a relatively narrow wavelength band of 380 to 770 nanometers, a general term would be "radiation pollution" so as to encompass all wavelengths of the electromagnetic spectrum. Public concern with the problem of radiation pollution is evidenced by the enactment of Public Law No. 90-602 known as the "Radiation Control for Health and Safety Act of 1968." This act is designed to study and control "electronic product radiation" and covers "any ionizing or nonionizing electromagnetic or particulate radiation."
In the range of visible light, energy distortion of an artificial light source as compared with a standard such as natural sunlight, can be measured quite accurately by use of a spectrophotometer. With the aid of such measurements, light sources have been designed which emit visible light approximating natural daylight in spectral composition. Recently fluorescent lamps have become commercially available having light-emitting phosphors providing a spectral balance closer to natural light.
With respect to radiation pollution occurring outside the range of visible light, e.g., ultraviolet, infrared, X-rays, cosmic rays, etc., the problem of detecting radiation distortions and their biological effects is much more difficult. One reason for the difficulty is that measurement of such radiations by conventional measuring methods, particularly at low energy levels, is not precise. Another reason is the difficulty in determining the long-term effects of low energy radiation distortion at various wavelengths.
Extensive studies by the inventor of plant growth under artificial light sources using time-lapse photography techniques have revealed that plants are very sensitive indicators of artificial radiation distortion. Lights used for photographic purposes having radiation deficiencies and distortions compared with natural light caused a variety of physiological responses in plants. For example, one type of photographic light resulted in the development of all male buds on a pumpkin vine whereas a different type of light resulted in the development of all female buds. It has been shown that radiation distortion affecting plants may also influence physiological growth responses in animals. Thus, it has been demonstrated that the sex ratio of guppies and mice born of parents kept under different types of artificial light is affected. Still further, it is now known that light entering the eyes of human beings triggers the release of hormones affecting body chemistry and that the effect is dependent on the wavelength of light entering the eye.
One effect that has been noted is that unnatural radiation may affect the seed germination and growth rate of plants. By comparing the germination and growth rate of a group of seeds exposed to radiation being investigated with that of another group of seeds exposed to natural radiation, a reliable and effective way is provided for detection of radiation pollution.
Experiments performed by the inventor using plants grown under fluorescent lamps have revealed the existence of radiation from the electrode area of the lamp which is different from the radiation from the lamp phosphor coating which provides the illumination. Also, the experiments showed that such electrode radiation is a form of radiation pollution in that it produces abnormal growth responses of plants exposed to fluorescent lamps as a source of illumnination. Since fluorescent lamps are often used in greenhouses to expedite plant growth, it is desirable to eliminate such electrode radiation. The effect of electrode radiation from fluorescent lamps on animals and human beings is not known. However, since experiements have shown that unnatural radiation may produce abnormal growth responses in animals and human beings by affecting the endocrine system, it is believed to be desirable for health reasons to eliminate as far as possible all sources of radiation pollution including electrode radiation from fluorescent lamps.
Accordingly, it is an object of the present invention to provide an improved fluorescent lamp constructed to prevent emission of electrode radiation.
Another object of the invention is to provide a fluorescent lamp and housing construction having a grounded shield adjacent the electrodes designed and located so as to prevent emission from the lamp of electrode radiation without substantial interference with the emission of the illuminating light produced by the lamp phosphors.
A further object of the invention is to provide an inexpensive grounded radiation shield and housing construction that can be easily applied to fluorescent lamp fixtures to reduce or eliminate emission from the lamps of electrode radiation.
Further objects and advantages of the invention will become apparent as the following description proceeds.